Strained Si/SiGe/SOI islands and processes of making same

ABSTRACT

A process of making a strained silicon-on-insulator structure is disclosed. A recess is formed in a substrate to laterally isolate an active area. An undercutting etch forms a bubble recess under the active area to partially vertically isolate the active area. A thermal oxidation completes the vertical isolation by use of a minifield oxidation process. The recess is filled to form a shallow trench isolation structure. An active device is also disclosed that is achieved by the process. A system is also disclosed that uses the active device.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. application Ser. No.10/634,174, filed on Aug. 5, 2003 now U.S. Pat. No. 7,153,753, which isincorporated herein by reference.

This application is related to the following commonly assigned U.S.patent applications which are herein incorporated by reference in theirentirety: “Output Prediction Logic Circuits With Ultra-Thin VerticalTransistors and Methods of Formation,” U.S. application Ser. No.10/164,611, filed on Jun. 10, 2002; “Micro-Mechanically StrainedSemiconductor Film,” U.S. application Ser. No. 10,379,749, filed on Mar.5, 2003; “Localized Strained Semiconductor on Insulator,” U.S.application Ser. No. 10/425,797, filed on Apr. 29, 2003; “StrainedSemiconductor By Wafer Bonding with Misorientation,” U.S. applicationSer. No. 10/425,484, filed on Apr. 29, 2003; “Micromechanical StrainedSilicon By Wafer Bonding,” U.S. application Ser. No. 10,431,137, filedon May 7, 2003; and “Strained Si/SiGe Structures by Ion Implantation,”U.S. application Ser. No. 10/431,134, filed on May 7, 2003.

TECHNICAL FIELD

This disclosure relates generally to semiconductor structures, and moreparticularly, to strained silicon-on-insulator (SSOI) structures.

BACKGROUND

One area of interest for improving the speed and performance ofsemiconductor devices includes strained silicon technology, which hasbeen shown to enhance carrier mobility in both n-channel and p-channeldevices, and is being considered to improve the electron mobility anddrift velocity in n-channel MOSFETs in complementary metal oxidesemiconductor (CMOS) technology.

There has been considerable research using strained silicon germaniumlayers on silicon to increase the hole mobility of p-channel CMOStransistors. Thin layers of silicon germanium have been fabricated onsilicon because of the tolerance of the thin silicon germanium layers tostrain.

Solid phase epitaxial (SPE) regrowth of silicon on sapphire is known.The SPE regrowth of silicon reduces defects and dislocations that occurduring the initial epitaxial deposition of silicon on sapphire becauseof a large lattice mismatch. A silicon implant amorphizes the initialsilicon layer, and regrowth is accomplished at a low temperature.Subsequently, strained layers of silicon germanium have been grown onsilicon by SPE.

Silicon germanium layers have been grown on silicon by ion implantationand regrowth by laser melting. Silicon germanium layers have also beenformed by ion implantation and regrowth by SPE. The use of ionimplantation to form silicon germanium layers, and the use of SPE toregrow layers of silicon germanium on silicon have been describedseparately and in combination with one another.

Thin layers of strained silicon are being considered for CMOS n-channeldevices. Thinner layers of silicon are more tolerant of strain. Onetechnique for producing strained silicon involves epitaxially growingthe silicon and silicon germanium layers using an ultra-high vacuumchemical vapor deposition (UHVCVD) process, a costly and complexprocess, to form silicon layers on relaxed silicon germanium layers. Alarge mismatch in the cell structure causes a pseudo-morphic layer ofsilicon on relaxed silicon germanium to be under biaxial tensile strain.The biaxial strain modifies the band structure and enhances carriertransport in the silicon layer.

The strain on the silicon layer depends of the lattice constantdifference between silicon and silicon germanium. The lattice constantof silicon germanium is between the lattice constant of silicon (5.43095Å) and the lattice constant of germanium (5.64613 Å), and depends on thepercentage of germanium in the silicon germanium layer.

There is a need in the art to provide improved methods of formingstrained silicon structures to improve the speed and performance ofsemiconductor devices such as CMOS n-channel devices.

SUMMARY

The above mentioned problems and challenges are overcome by embodimentsof this invention. One embodiment is directed to a process of forming avertically isolated strained silicon-on-insulator (SSOI) structure ofsufficient size to permit the fabrication of an active device thereon.One embodiment of the process includes forming an etch-selective regionin the semiconductive workpiece that restricts the effects of anisotropic etch. The etch-selective region is created by implantationthat causes the semiconductive material to become amorphous.

Protective material, such as a polysilicon layer and a nitride layer, isdeposited over a pad oxide layer to protect the pad oxide layer. Anactive area is defined by patterning a mask. The protective material,the pad oxide layer, and finally the substrate are etched to form atrench around the active area. A protective film such as nitridematerial, is formed upon exposed silicon. An isotropic etch follows thatacts to substantially insulate the active area by its undercuttingeffect. Thereafter, an oxidation process is done to totally isolate theactive area from adjacent active areas and the substrate. Oxide spacersare formed on the sides of the active area, and the remainder of thetrench is filled to form a shallow trench isolation (STI) structure.

Because the diode junctions of active devices are formed in areas of thesubstrate that are isolated from the remainder of the substrate, thediode junctions are fabricated to be less leaky.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the manner in which embodiments are obtained, a moreparticular description of the embodiments briefly described above willbe rendered by reference to specific embodiments which are illustratedin the appended drawings. These drawings depict embodiments that are notnecessarily drawn to scale and are not to be considered to be limitingof its scope. The claimed subject matter will be described and explainedwith additional specificity and detail through the use of theaccompanying drawings in which:

FIG. 1A is a side cross-section of a semiconductive structure accordingto an embodiment;

FIG. 1B is a side cross-section of the structure depicted in FIG. 1Aafter further processing;

FIG. 1C illustrates the structure depicted in FIG. 1B after furtherprocessing;

FIG. 1D is a side cross-section of the structure depicted in FIG. 1Cafter further processing;

FIG. 1E illustrates further processing of the substrate depicted in FIG.1D;

FIG. 1F illustrates further processing of the substrate depicted in FIG.1E;

FIG. 2A is a side cross-section of a semiconductor structure accordingto an embodiment;

FIG. 2B illustrates further processing of the substrate depicted in FIG.2A;

FIG. 3A is a side cross-section of a semiconductor structure accordingto an embodiment;

FIG. 3B is a side cross-section of the structure depicted in FIG. 3Aafter further processing;

FIG. 4A is a side cross-section of a semiconductor structure accordingto an embodiment;

FIG. 4B is a side cross-section of the structure depicted in FIG. 4Aafter further processing;

FIG. 4C is a side cross-section of the structure depicted in FIG. 4Bafter further processing

FIG. 4D is a side cross-section of the structure depicted in FIG. 4Cafter further processing;

FIG. 4E is a side cross-section of the structure depicted in FIG. 4Dafter further processing;

FIG. 5 is a top view of a wafer or substrate containing semiconductordies in accordance with an embodiment;

FIG. 6 is a block diagram of a circuit module in accordance with anembodiment;

FIG. 7 is a block diagram of a memory module in accordance with anembodiment;

FIG. 8 is a block diagram of an electronic system in accordance withanother embodiment the present invention;

FIG. 9 is a block diagram of a memory system in accordance with anembodiment; and

FIG. 10 is a block diagram of a computer system in accordance with anembodiment.

DETAILED DESCRIPTION

The following detailed description refers to the accompanying drawingsthat show, by way of illustration, specific aspects and embodiments inwhich various embodiments may be practiced. The various embodiments arenot necessarily mutually exclusive as aspects of one embodiment can becombined with aspects of another embodiment. Other embodiments may beutilized and structural, logical, and electrical changes may be madewithout departing from the scope of the claimed subject matter.

In the following description, the terms wafer and substrate areinterchangeably used to refer generally to any structure on whichintegrated circuits are formed, and also to such structures duringvarious stages of integrated circuit fabrication. Both terms includedoped and undoped semiconductors, epitaxial layers of a semiconductor ona supporting semiconductor or insulating material, combinations of suchlayers, as well as other such structures that are known in the art. Theterms wafer and substrate used in the following description include anystructure having an exposed surface with which to form the integratedcircuit (IC) structure relating to claimed subject matter. The termsubstrate is understood to include semiconductor wafers. The termsubstrate is also used to refer to semiconductor structures duringprocessing, and may include other layers that have been fabricatedthereupon. Both wafer and substrate include doped and undopedsemiconductors, epitaxial semiconductor layers supported by a basesemiconductor or insulator, as well as other semiconductor structureswell known to one skilled in the art. The term conductor is understoodto include semiconductors, and the term insulator or dielectric isdefined to include any material that is less electrically conductivethan the materials referred to as conductors.

The terms “horizontal” and “vertical”, as well as prepositions such as“on”, “above”, “below”, “over” and “under” are used in relation to theconventional plane or surface of a wafer or substrate, regardless of theorientation of the wafer or substrate. The following detaileddescription is, therefore, not to be taken in a limiting sense, and thescope of the present invention is defined only by the appended claims,along with the full scope of equivalents to which such claims areentitled.

Strained silicon is provided using an improved method for forming astrained silicon layer on a silicon germanium structure. One improvedmethod embodiment includes implanting germanium ions into a siliconsubstrate, and performing an SPE process to regrow a crystalline siliconlayer over a resulting silicon germanium layer in the substrate.

FIG. 1A is a side cross-section of a semiconductive structure accordingto an embodiment. A substrate 110 is provided that includes asemiconductive material. The substrate 110 has a pad oxide layer 112deposited thereon. As used herein, the term deposited is used broadly tomean layers that are not only deposited in the traditional sense, butlayers of material that are grown or in any other manner caused to beformed. A protective layer 114 is deposited on top of the pad oxidelayer 112 to act as a buffer during subsequent etch steps and otherprocessing. In one embodiment, the protective layer 114 is polysilicon.In one embodiment, the protective layer 114 is a nitride material. Inanother embodiment, the protective layer 114 is a polysilicon layer thatis covered with a nitride material. The specific combination is selecteddepending upon process integration choices, among other design choices.

Below the pad oxide layer 112, a strained silicon layer 116 has beenformed above a semiconductive silicon compound that is a relaxed or asemi-relaxed layer 118 (hereinafter “relaxed layer”). Strained siliconis provided using a method for forming a strained silicon layer on asilicon compound structure. In one embodiment, a silicon germaniumstructure is the relaxed layer 118. Other silicon-compound structurescan be used according to a specific process integration. In oneembodiment, the process includes implanting germanium ions into asilicon substrate 110, and performing a solid-phase epitaxy (SPE)process to regrow a crystalline silicon layer over a resulting silicongermanium layer in the substrate 110.

FIG. 1A illustrates the result of a method of forming a strained siliconlayer 116 on a silicon germanium (Si/SiGe) structure 118 (that laterbecomes the relaxed layer 118) by ion implantation, according to variousembodiments. In one embodiment, germanium ions are implanted into ap-type silicon wafer 110, as represented in FIG. 1A. In variousembodiments, the dose of the germanium ion implant is approximately10¹⁷/cm², and the energy of the germanium ion implant is less than 200KeV.

As depicted in FIG. 1A, the relatively high dose and energy of thegermanium ion implant, that becomes the relaxed layer 118, in thesilicon substrate 110 results in a region of silicon that containsgermanium ions, represented as 118, on the silicon substrate 110.Formation of the relaxed layer 118 further results in an amorphized, orat least a partially amorphized, silicon layer 116 at the surface. Invarious embodiments, if the germanium ion implant did not completelyamorphize the silicon layer 116, a silicon ion implant is used tofurther amorphize the silicon layer 116. In various embodiments, thedose of this silicon ion implant to amorphize the silicon layer 116 isapproximately 10¹⁵/cm² and the energy of this silicon ion implant isless than 170 KeV.

During an ion implantation process, the ions can channel along thecrystal directions of the substrate 110, such that the ions do notencounter nuclei and are slowed down mainly by electronic stopping.Channeling can be difficult to control, and can cause the ions topenetrate several times deeper than intended. In various embodiments, toavoid channeling during the germanium ion implant, the substrate 110 isamorphized using a silicon ion implant to prepare the substrate for thegermanium ion implant. In various embodiments, the dose of this siliconion implant is approximately 10¹⁵/cm² and the energy of this silicon ionimplant is greater than 50 KeV. Preparing the substrate 110 using thesilicon ion implant to amorphize the substrate 110 results in betterdepth control during the germanium ion implant process. In oneembodiment, the implant is disposed below the germanium ion implant, andit is used as a deep implantation (such as lower deep implant 211, FIG.2A) as discussed below.

After implanting to form the germanium ion implant that becomes therelaxed layer 118, the substrate 110 is heat treated, such that theamorphized layers are regrown by a solid phase epitaxy (SPE) process. Invarious embodiments, the SPE process involves heating the structures attemperatures within a range of approximately 550° C. to 700° C. for atime within a range from approximately one hour to approximately twohours. The resulting substrate 110 includes the silicon region thatcontains germanium ions, forms a silicon germanium (Si_(1−x)Ge_(x))relaxed layer 118, and the amorphous silicon layer 116 regrows into amore crystalline strained silicon layer 116 over the silicon germaniumrelaxed layer 118. In various embodiments, the strained silicon layer116 is approximately 20 nm thick. However, the present invention is notlimited to a particular thickness. The thickness of the strained siliconlayer 116 is controlled by the energy of the implant. One of ordinaryskill in the art will understand, upon reading and comprehending thisdisclosure, how to control the germanium implant to achieve a desiredthickness of the strained silicon layer 116.

The lattice mismatch of the strained silicon layer 116 at the surfacewith the underlying silicon germanium relaxed layer 118 causes thestrained silicon layer 116 to be strained. In various embodiments,N-channel CMOS devices are fabricated in this strained silicon layer 116using conventional techniques, which are not described here for the sakeof brevity.

One of ordinary skill in the art will understand, upon reading andcomprehending this disclosure, that the concentration of germanium inthe relaxed layer 118 is controlled by the dose and energy of thegermanium ion implant process. Additionally, one of ordinary skill inthe art will understand, upon reading and comprehending this disclosure,that the concentration of germanium in the relaxed layer 118 can begraded by controlling the dose and energy of two or more germanium ionimplant process. A benefit of grading germanium concentration involvesforming a silicon germanium layer 118 on the substrate 110 to have arelaxed silicon germanium surface upon which the strained silicon layer116 is formed.

According to further processing, a mask 120 is formed and patterned uponthe protective layer 114. In one embodiment, the mask 120 is aphotoresist material that is spun on, exposed, cured, and patterned. Inanother embodiment, the mask 120 is a hard mask material such as anitride or oxide. The area protected by the mask 120 defines what willbecome an active area in a strained silicon-on-insulator (SSOI)structure (hereinafter, “SSOI active area”).

FIG. 1B is a side cross-section of the structure depicted in FIG. 1Aafter further processing. FIG. 1B illustrates an embodiment after anetch process that has exposed the regions unprotected by the mask 120.In the etch process, the protective layer 114 and the pad oxide layer112 have also been patterned, and a recess 122 has been formed with arecess bottom 124 and a recess wall 126. In one embodiment, the etch isanisotropic.

FIG. 1C illustrates the structure depicted in FIG. 1B after furtherprocessing. A nitride film 128 has been grown onto the exposedsemiconductive material of the substrate 110 and elsewhere. In oneembodiment, the exposed semiconductive material of the substrate 110 isexposed silicon. The nitride film 128 is depicted as covering the recessbottom 124, the recess wall 126, and the protective layer 114. Thenitride film 128 may be grown by known processes under conditions thatdeposit only upon semiconductive material such as exposed silicon. Onesuch process is remote-plasma nitridation (RPN). In RPN, anitride-bearing plasma is struck, remote from substrate 110, but withinthe deposition tool, and the nitride-bearing plasma is carried byconvective force toward the substrate 110. In one embodiment, an RPNprocess is carried out in a time range from about 10 seconds to about 10minutes. In another embodiment, an RPN process is carried out in a timerange from about 1 minute to about 3 minutes. Another process that maybe used to form the nitride film 128 is rapid thermal nitridation (RTN).Such processing is also known in the art.

Alternative to the formation of a nitride film 128, an oxide film may beformed, either by remote-plasma oxidation (RPO) or by rapid thermaloxidation (RTO). Similarly, a combination of an oxide and a nitride isformed according to an embodiment as set forth herein. In oneembodiment, the placement of the oxide precedes the placement of thenitride, or vice versa. Similarly, an oxynitride film is formed in theplace of the nitride film 128 according to an alternative embodiment.The process is carried out by either a remote plasma process or a rapidthermal process. Although not limiting the embodiments disclosed, forconvenience throughout the remainder of the disclosure, the film 128 isreferred to as the “nitride film 128”.

FIG. 1D is a side cross-section of the structure depicted in FIG. 1Cafter further processing. FIG. 1D illustrates processing of thesubstrate 110 in which a spacer etch has formed a spacer 130 from thenitride film 128. The spacer etch is selective to not etch the materialin the recess 122 that forms the recess bottom 124. Therefore in oneembodiment, the recess bottom 124 is exposed in the spacer etch, but itis not significantly etched.

FIG. 1E illustrates further processing of the substrate 110 depicted inFIG. 1D. After the spacer etch, which formed the spacer 130, anisotropic etch forms a “bubble” recess 132 in the substrate 110. Theisotropic etch forms the bubble recess 132 in preparation for asubsequent oxidation process. The bubble recess 132 is depicted inarbitrary shape and size. Qualitative characteristics of the bubblerecess 132, however include an incomplete undercut of the material thatforms the relaxed layer 118. The extent of the etch to form the bubblerecess 132, qualitatively speaking, leaves enough material in thesubstrate 110 to prevent a total undercutting, but leaves enough toallow further processing without significant damage to the positioningof the relaxed layer 118.

In one embodiment, an etch recipe is used that is selective to thematerial of the relaxed layer 118 and to the protective layer 114, butthe etch recipe removes bulk semiconductive material in the substrate110. In one embodiment, the etch recipe is a wet tetramethyl ammoniumhydroxide (TMAH) etch as is known in the art. In another embodiment, thewet etch uses a potassium hydroxide (KOH) etch chemistry that is knownin the art. The TMAH etch chemistry is desirable because it is selectivesuch that it etches the bulk silicon of the substrate 110, but does notsubstantially etch the relaxed layer 118. In one embodiment, theselectivity is in a range from about 5:1 to about 20:1. In anotherembodiment, the selectivity is about 10:1. The isotropic etch may alsobe combined with an anisotropic etch, either before or after theisotropic etch. By using both an isotropic and an anisotropic etch, boththe downward etching and the undercutting of the relaxed layer 118 maybe varied to suit particular applications.

Various wet TMAH etch recipes are known that are selective todisturbed-lattice silicon such as the relaxed layer 118 andion-channeling-preventive layers, and to nitride films (or oxide films,or oxynitride films), and that isotropically etch bulk monocrystallinesilicon along crystallographic planes. FIG. 1E illustrates the resultsof a TMAH etch that has formed the bubble recess 132 that has undercutwhat will become the SSOI active area 134 (FIG. 1F). By thisundercutting etch, the active area has been mostly isolated from thebulk semiconductive material in the substrate 110, below the level ofthe relaxed layer 118.

Under the etch conditions, and due to the scale of the bubble recess132, a distinctive contour may appear therein. The TMAH etch has aneffect along crystallographic planes such that a faceted contour mayappear within the bubble recess 132. It can be seen that facetedsurfaces 132, 132′, 132″, 132′″, etc., are illustrated on one side.However, these are depicted in arbitrary shape, angle and size forillustrative purposes, and the specific shapes, angles, and sizes of thefaceted surfaces will depend upon the crystallographic orientation ofthe bulk semiconductive material in the substrate 110 and upon thespecific etch recipe and conditions, among other factors.

Under the specific etch conditions, a photomicrographic view of thebubble recess 132 depicts substended crystallographic planes of bulksemiconductive material in the substrate 110 that have been exposed byan etch such as the TMAH etch.

FIG. 1F illustrates further processing of the substrate 110 depicted inFIG. 1E to form a strained Si/SiGe/SOI island according to anembodiment. After the isotropic etch forms the bubble recess 132, anoxidation process is carried out to vertically isolate an SSOI activearea 134 by the formation of a mini-field oxidation (MFOX) 136. In oneembodiment, the oxidation process is carried out with the protectivelayer 114 and the spacers 130 in place (FIG. 1E), followed by a nitrideetch to remove them.

Oxidation time will depend upon the area of the partially isolatedstructure that includes the undercut relaxed layer 118. In oneembodiment, oxidation parameters include a processing temperature fromabout 850° C. to about 1,100° C. The ambient is with wet or dry oxygen(O₂), and atmospheric pressure or higher. In one example, a temperatureof about 850° C. and a wet oxygen ambient is applied at about 1atmosphere and for a sufficient time to allow about 0.1 micronhorizontal oxidation under the relaxed layer 118, and about 0.1 micronvertical oxidation upwardly in the direction of the relaxed layer 118.High pressure may be used to reduce the time required for oxidation andto control the amount of oxide that forms behind the nitride spacer 130.High pressure includes atmospheric pressure, up to about 2 atmospheresand higher including from about 2 to about 5 atmospheres.

Similar to the qualitative size and shape of the bubble recess 132, theMFOX 136 is also depicted in arbitrary shape and size. The actual sizeand shape of the MFOX 136 will be influenced by etch and oxidationconditions according to a process integration. One characteristic offorming the MFOX 136 requires an oxidation process that leaves the SSOIactive area 134 firmly attached to the substrate 110 through the MFOX136. By this process, oxidation is sufficient to vertically isolate thestrained silicon 112 from the substrate 110 to create the SSOI activearea 134. Processing conditions can be ascertained by reading thisdisclosure and by ordinary experimentation.

The oxidation process affects the integrity of the SSOI active area 134.For a 0.25-micron critical-dimension 138 (CD or minimum feature)process, the SSOI active area 134 has a height 140 in a range from about0.1 microns to about 0.15 microns. Alternatively, for a 0.15-micron CDprocess, the SSOI active area 134 has a height 140 in a range from about0.07 microns to about 0.12 microns.

According to an embodiment, the formation of the MFOX 136 is carried outunder conditions to prevent destructive stresses in the newly formedSSOI active area 134. One of ordinary skill in the art can conduct theminifield oxidation in the bubble recess 132 without causing destructivestresses in the SSOI active area 134.

FIG. 2A is a side cross-section of a semiconductor structure accordingto an embodiment. In this embodiment, a two-tiered deep implantation hasbeen carried out. The two-tiered deep implantation is done to facilitatea more lateral isotropic etch than the etch depicted in FIG. 1E. Thetwo-tiered implantation can also assist as anti-channeling processing.FIG. 2A is depicted at a processing flow similar to the structuredepicted in FIG. 1A, with the additional processing of the two-tiereddeep implantation.

In one embodiment, the deep implantations 209 and 211 form layers in thebulk semiconductive material in the substrate 210. Implantation iscarried out at an energy level that achieves self-interstitialimplantation, and that causes the deep implantations 209 and 211 tobecome amorphous enough to have an etch responsiveness that is differentfrom the bulk semiconductive material in the substrate 210. In oneembodiment, implantation conditions use a silicon source that isimplanted to a monocrystalline-to-self interstitial ratio of about 3:1.By “silicon source” it is meant in one embodiment that silicon oranother Group IV element is used, or a combination such as silicon andgermanium. In one embodiment, the implanted concentration is from about10¹⁴/cm² to about 5×10¹⁵/cm² at process conditions of ambienttemperature (20 C to about 30 C) and an implantation energy of greaterthan about 50 KeV. In one embodiment, a silicon source that issubstantially equivalent to the silicon chemistry of the bulk of thesemiconductive substrate 210, is implanted to a concentration of about10¹⁴/cm² and process conditions are about 25 C and an implantationenergy of about 85 KeV.

A substrate 210 is provided that includes a semiconductive material. Theupper deep implantation 209 and the lower deep implantation 211 areprovided for subsequent processing. The substrate 210 also has a padoxide layer 212 deposited thereon. A protective layer 214 is depositedon top of the pad oxide layer 212 to act as a buffer during subsequentetch steps and other processing. The protective layer 214 can be any ofthe disclosed protective layers depicted and described for theembodiments illustrated in FIGS. 1A-1F, and their art-recognizedequivalents that are understood by reading this disclosure.

Below the pad oxide layer 212, a strained silicon layer 216 has beenformed above a relaxed or semi-relaxed layer 218 (hereinafter, relaxedlayer 218). The relaxed layer 218 can be a semiconductor compoundsilicon layer. In one embodiment, a silicon germanium structure is therelaxed layer 218. Other silicon-compound structures can be usedaccording to a specific process integration.

According to a process flow embodiment, the substrate 210 is implantedwith the relaxed layer 218, at least the lower deep implantation 211 andthe upper deep implantation 209. The pad oxide layer 212 and theprotective layer 214 are patterned with the mask 220. An etch is carriedout to form a recess (222, FIG. 2B) that is similar to the recess 122depicted in FIG. 1B. Thereafter, a nitride film (not pictured) is grownand spacer etched similar to the respective nitride film 128 and spacer130 depicted in FIGS. 1C and 1D.

Subsequent to a spacer etch, a “flattened bubble” recess (not pictured)is formed by an isotropic etch. The flattened bubble is formed becauseof the upper deep implantation 209 and the lower deep implantation 211.In this embodiment, the etch recipe that is used is more selective toleaving the upper deep implantation 209 and the lower deep implantation211. Consequently, the flattened bubble recess is formed due to theconstraining nature of the upper deep implantation 209 and the lowerdeep implantation 211 upon the etch. The extent of the etch to form theflat bubble, qualitatively speaking, leaves enough material in thesubstrate 210 to prevent a total undercutting, but leaves enough toallow further processing without significant damage to the positioningof the relaxed layer 218. In one embodiment, the etch is carried outwithout an upper deep implantation 209, and the relaxed layer 218 hassufficient responsiveness to an undercutting etch to be selectively etchresistant, relative to the bulk material of the substrate 210.

FIG. 2B illustrates further processing of the substrate 210 depicted inFIG. 2A to form a strained Si/SiGe/SOI island according to anembodiment. After the isotropic etch forms the flat bubble recess (notpictured), an oxidation process is carried out to vertically isolate anSSOI active area 234 by the formation of a flattened mini-fieldoxidation (FMFOX) 236. In one embodiment, the oxidation process iscarried out with the protective layer 214 and the spacers (not pictured)in place, followed by a nitride etch to remove them.

Similar to the shape of the MFOX 136 (FIG. 1F), the size and shape ofthe FMFOX 236 is also depicted in arbitrary shape and size. The actualsize and shape of the FMFOX 236 will be influenced by etch and oxidationconditions according to the placement of the upper deep implantation 209and the lower deep implantation 211, their relative responses to a givenetch recipe, and the extent of the oxidation process. One characteristicof forming the FMFOX 236 requires an oxidation process that leaves theSSOI active area 234 firmly attached to the substrate 210 through theFMFOX 236. By this process, oxidation is sufficient to verticallyisolate the relaxed layer 218 from the substrate 210 to create the SSOIactive area 234. Processing conditions can be ascertained by ordinaryexperimentation.

The oxidation process affects the integrity of the SSOI active area 234.For a 0.25-micron CD 238 process, the SSOI active area 234 has a height240 in a range from about 0.1 microns to about 0.15 microns.Alternatively, for a 0.15-micron CD process, the SSOI active area 234has a height 240 in a range from about 0.07 microns to about 0.12microns.

According to an embodiment, the formation of the. FMFOX 236 is carriedout under conditions to prevent destructive stresses in the newly formedSSOI active area 234. By reading this disclosure, one of ordinary skillin the art can conduct the minifield oxidation in the flattened bubblerecess without causing destructive stresses in the SSOI active area 234.

FIG. 3A is a side cross-section of a semiconductor structure accordingto an embodiment. In this process flow embodiment, a bubble recess 332has been formed in a substrate 310, below a protective layer 314 that isformed upon an oxide film 312. Positioning of the bubble recess 332 iscontrolled by a spacer 330, which is formed according to processingembodiments set forth in this disclosure.

FIG. 3B is a side cross-section of the structure depicted in FIG. 3Aafter further processing to form a strained Si/SiGe/SOI island accordingto an embodiment. After the isotropic etch forms the bubble recess 332,an oxidation process is carried out to vertically isolate an SSOI activearea which will become the relaxed region 318 by the formation of anMFOX 336 or an FMFOX 336. In one embodiment, the oxidation process iscarried out with the protective layer 314 and the spacers 330 in place,followed by a nitride etch to remove them.

Similar to the bubble recess 332, the size and shape of the MFOX 336 orthe FMFOX 336 is also depicted in arbitrary shape and size. The actualsize and shape of the MFOX 336 or the FMFOX 336 will be influenced byetch and oxidation conditions according to a process integration. Onecharacteristic of forming the MFOX 336 or the FMFOX 336, requires anoxidation process that leaves the SSOI active area 318 firmly attachedto the substrate 310 through the MFOX 336 or the MFOX 336. By thisprocess, oxidation is sufficient to vertically isolate the SSOI activearea 318 from the substrate 310 to create an SOI structure. Processingconditions can be ascertained by ordinary experimentation.

The oxidation process affects the integrity of the SSOI active area 318.For a 0.25-micron CD 338 process, the SSOI active area 318 has a heightin a range from about 0.1 microns to about 0.15 microns. Alternatively,for a 0.15-micron CD process, the SSOI active area 318 has a height in arange from about 0.07 microns to about 0.12 microns.

According to an embodiment, the formation of the MFOX 336 or the FMFOX336 is carried out under conditions to prevent destructive stresses inthe newly formed SSOI active area 318. One of ordinary skill in the artcan read this disclosure and by routine experimentation, conduct themini field oxidation without causing destructive stresses in the SSOIactive area 318.

After the formation of the MFOX 336 or the FMFOX 336, a strained siliconlayer 316 is formed above the SSOI active area which may now be viewedas a relaxed region 318 according to processing embodiments disclosedherein. This process flow path includes what may be referred to as a“top-down” formation of the strained silicon layer 316, as ionimplantation 317 is used. In the next embodiment, a “bottom-up”formation of a stressed silicon film is disclosed.

FIG. 4A is a side cross-section of a semiconductor structure accordingto an embodiment. This process flow is referred to as bottom-upformation of a strained silicon layer. In this process flow embodiment,a bubble recess (not pictured) has been formed in a substrate 410, belowa protective layer (not pictured) that is formed upon an oxide film (notpictured). Positioning of the bubble recess is controlled by a spacer(not pictured), which is formed according to processing embodiments setforth in this disclosure. An MFOX 436 or an FMFOX 436 is formedaccording to processing embodiments set forth in this disclosure, whichsimultaneously forms an active area precursor 433.

FIG. 4B is a side cross-section of the structure depicted in FIG. 4Aafter further processing. After the isotropic etch forms the bubblerecess, an oxidation process is carried out to vertically isolate theactive area precursor 433 by the formation of the MFOX 436 or the FMFOX436. In one embodiment, the oxidation process is carried out with theprotective layer and the spacers in place, followed by a nitride etch toremove them.

Similar to the bubble recess 132 (FIG. 1E), the size and shape of theMFOX 436 or the FMFOX 436 is also depicted in arbitrary shape and size.The actual size and shape will be influenced by etch and oxidationconditions according to a process integration. One characteristic offorming the MFOX 436 or the FMFOX 436, requires an oxidation processthat leaves the active area precursor 433 firmly attached to thesubstrate 410 through the MFOX 436 or the FMFOX 436. By this process,oxidation is sufficient to vertically isolate the active area precursor433 from the substrate 410 to create an SOI structure. Processingconditions can be ascertained by reading this disclosure, and by routineexperimentation.

In this process flow embodiment, the active area precursor 433 is usedto grow a relaxed layer 418 and a strained silicon layer 416. In oneprocess embodiment, a CVD process is used. In one process embodiment, anultra-high vacuum CVD (UHV CVD) process is used.

FIG. 4B depicts the formation of an epitaxial relaxed layer 418, anepitaxial strained silicon layer 416, and a polycrystalline zone 417that is doped similarly to the respective epitaxial relaxed layer 418and the epitaxial strained silicon layer 416. The solid vertical arrows415 represent epitaxial, bottom-up growth of the epitaxial relaxed layer418 and the epitaxial strained silicon layer 416. The dashed verticalarrows 413 represent, bottom-up growth of the polycrystalline zone 417.

FIG. 4C is a side cross-section of the structure depicted in FIG. 4Bafter further processing. An etch recipe is used that is selective toleaving the epitaxial and crystalline silicon in the strained siliconlayer 416, the relaxed layer 418, and the substrate 410. The etch reciperemoves the polycrystalline zone 417 (FIG. 4B), and leaves the SSOIactive area 434 as depicted.

The oxidation process affects the integrity of the SSOI active area 434.For a 0.25-micron CD 438 process, the SSOI active area 434 has a height440 in a range from about 0.1 microns to about 0.15 microns.Alternatively, for a 0.15-micron CD process, the SSOI active area 434has a height 440 in a range from about 0.07 microns to about 0.12microns.

According to an embodiment, the formation of the MFOX 436 or the FMFOX436 is carried out under conditions to prevent destructive stresses inthe newly formed SSOI active area 434. By reading this disclosure, oneof ordinary skill in the art can conduct the minifield oxidation byroutine experimentation without causing destructive stresses in the SSOIactive area 434.

FIGS. 4D and 4E illustrate further processing according to an embodimenttaken from the structure depicted in FIG. 4C by way of non-limitingexample. The processing depicted in FIGS. 4D and 4E, however, is alsoapplicable to the structures depicted in FIGS. 1F, 2B, and 3B.

The vertically and laterally isolated SSOI active areas 434, alsoreferred to as Si/SiGe/SOI islands 434 according to one embodiment, areseparated by the recess 422 that, in this embodiment, acts as a shallowtrench isolation (STI) trench. According to an embodiment, the recess422 is filled with a material such as oxide by a known process such as ahigh-density plasma (HDP) technique. In one embodiment, the substrate410 is blanket HDP deposited with an oxide blanket 454 deposition, whichblankets the substrate 410 and which partially fills the recess 422.Thereafter, the oxide blanket 454 is etched back to form a spacer 454.The spacer 454 and the oxide fill 456 form a shallow trench dielectric.Next, an oxide fill 456 is carried out, and etched back by a processthat stops on a protective layer 412 such as a pad oxide layer 412 oreven a polysilicon layer 412. Where the protective layer 412 is presentas a polysilicon material, overetching of the oxide fill 456 may occur.The etchback is carried out according to process needs, such as bychemical-mechanical polishing (CMP), mechanical polishing (MP), chemicaletchback, and others.

Another embodiment occurs where no protective layer 412 has remainedduring processing to this extent of the process. For example, where theprotective layer 412 is a nitride material, it is removed simultaneouslywith the remnant of the nitride protective film if present.

As depicted in FIG. 4D, the material filling the recess 422 is etched orplanarized so that the top surface 455 of the oxide spacer 454 and theoxide fill 456 is approximately even with the top surface of the padoxide layer 412. Where a protective layer is present such as apolysilicon material, the remnant of the protective layer is stripped ina manner so as not to damage the remnant of the pad oxide layer 412. Inone embodiment, the remnant of the pad oxide layer 412 is used as a gateoxide for the fabrication of active devices above the SSOI active area434.

Total isolation between devices on the SSOI active area 434 can be asmuch as 0.65 microns (0.2 microns of the oxide spacer 454 and oxide fill456, plus 0.25 microns of the SSOI active area 434, plus 0.2 microns ofthe oxide spacer 454 and oxide fill 456) for a given 0.25-micronlithography.

A portion of the structure depicted in FIG. 4D is also depicted in FIG.4E as a storage device, wherein two dynamic random access (DRAM) memorycells are formed thereon. Active devices in the form of a digit linejunction 458 and storage node junctions 460 and 462 are formed in thevertically isolated SSOI active area 434. A word line 464 overlays theSSOI active area 434. The storage node junctions 460 and 462 are inelectrical contact with respective capacitors 466 and 468 throughpolysilicon plugs 470. The digit line junction 458 is in electricalcontact with a polysilicon plug 472. The polysilicon plug 472 is acontact that touches the SSOI active area 434. The polysilicon plug 472is in further contact with a digit line 474 through a metal plug 476.

The substrate 410 carrying a vertically and laterally isolated SSOIactive area 434 provides a vehicle for the fabrication of a storagedevice such as a DRAM cell, or virtually any type of logic circuit thatemploys a MOSFET.

While the structure depicted in FIG. 4E illustrates one type of devicethat might be fabricated upon the workpiece of the substrate 410 andwith the use of the SSOI active area 434, those of ordinary skill in theart will recognize the advantages of fabricating other types of devicesaccording to various embodiments and their equivalents. In particular,active devices formed in the SSOI active area 434 will be substantiallyisolated from the bulk of the substrate 410.

The processes and structures that are achieve in the various embodimentsare inventively applicable to a variety of devices and apparatuses.System embodiments may be made by process embodiments, or that includean embodiment or embodiments of the structure. For example, a chippackage may contain an SSOI active area such as an active area set forthin this disclosure. In one embodiment, an array of SSOI active areas isincluded such as a line of sense amplifiers that use the active areas,or a 2-dimensional array of storage devices such as a DRAM array. Inanother embodiment, the SSOI active area is part of an electrical devicethat includes the semiconductor substrate in a chip package and the chippackage is part of a memory module or part of a chipset. In anotherembodiment, the memory module is part of a dynamic random access memorymodule that is inserted into a host such as a motherboard or a digitalcomputer. In another embodiment, systems are made that include the SSOIactive area. For example, a chip package may contain an SSOI active areasuch as one set forth in this disclosure. In another embodiment, theSSOI active area is part of an electrical device that includes thesemiconductor substrate in a chip package and the chip package is partof a memory module or part of a chipset. In another embodiment, thememory module is part of a dynamic random access memory module that isinserted into a host such as a motherboard or a digital computer. Inanother embodiment, the SSOI active area is part of an electronicsystem. In another embodiment, the SSOI active area is fabricated with afloating gate. In another embodiment, the SSOI active area is fabricatedwith a floating gate that is part of a flash memory device that in turnis part of a chipset such as a basic input-output system (BIOS) for anelectrical device.

FIG. 5 is a depiction of another embodiment. In this embodiment, systemsare made that include the SSOI active area. With reference to FIG. 5, asemiconductor die 510 is produced from a silicon wafer 500 that containsat least one of the SSOI active areas 134, 234, 334, and 434,respectively, such as are depicted in FIGS. 1F, 2B, 3B, 4C, and 4E. Adie 510 is an individual pattern, typically rectangular, on a substratesuch as substrate 110, substrate 210, substrate 310, or substrate 410that contains circuitry to perform a specific function. A semiconductorwafer 500 will typically contain a repeated pattern of such dies 510containing the same functionality. Die 510 may further containadditional circuitry to extend to such complex devices as a monolithicprocessor with multiple functionality. Die 510 is typically packaged ina protective casing (not shown) with leads extending therefrom (notshown) providing access to the circuitry of the die 510 for unilateralor bilateral communication and control. In one embodiment, die 510 isincased in a host such as a chip package (not shown) such as achip-scale package (CSP).

FIG. 6 is a depiction of another embodiment. As shown in FIG. 6, two ormore dies 510 at least one of which contains at least one of the SSOIactive areas 134, 234, 334, and 434, respectively, such as are depictedin FIGS. 1F, 2B, 3B, 4C, and 4E, in accordance with various embodimentsis combined, with or without a protective casing, into a host such as acircuit module 600 to enhance or extend the functionality of anindividual die 510. Circuit module 600 may be a combination of dies 510representing a variety of functions, or a combination of dies 510containing the same functionality. Some examples of a circuit module 600include memory modules, device drivers, power modules, communicationmodems, processor modules and application-specific modules and caninclude multi-layer, multi-chip modules. In one embodiment, the circuitmodule 600 is a sub-component of a variety of electronic systems, suchas a clock, a television, a cell phone, a personal computer, anautomobile, an industrial control system, an aircraft, a hand-held, andothers. In one embodiment, the circuit module 600 has a variety of leads610 extending therefrom providing unilateral or bilateral communicationand control. In another embodiment, circuit module 600 has a storagedevice such as is depicted in FIG. 4E.

FIG. 7 is a depiction of another embodiment. FIG. 7 shows one embodimentof a circuit module as memory module 700 containing a structure for theinventive SSOI active area such as are depicted in FIGS. 1F, 2B, 3B, and4C, or the storage device as is depicted in FIG. 4E. Memory module 700is a host for a configuration that generally depicts a Single In-lineMemory Module (SIMM) or Dual In-line Memory Module (DIMM). A SIMM orDIMM may generally be a printed circuit board (PCB) or other supportcontaining a series of memory devices. While a SIMM will have a singlein-line set of contacts or leads, a DIMM will have a set of leads oneach side of the support with each set representing separate I/Osignals. Memory module 700 contains multiple memory devices 710contained on support 715, the number depending upon the desired buswidth and the desire for parity. Memory module 700 may contain memorydevices 710 on both sides of support 715. Memory module 700 accepts acommand signal from an external controller (not shown) on a command link720 and provides for data input and data output on data links 730. Thecommand link 720 and data links 730 are connected to leads 740 extendingfrom the support 715. Leads 740 are shown for conceptual purposes andare not limited to the positions shown in FIG. 7.

FIG. 8 shows another host type such as an electronic system 800containing one or more circuit modules 600 as described above containingat least one of the SSOI active areas or data storage devices thatcontain such. Electronic system 800 generally contains a user interface810. User interface 810 provides a user of the electronic system 800with some form of control or observation of the results of theelectronic system 800. Some examples of user interface 810 include thekeyboard, pointing device, monitor and printer of a personal computer;the tuning dial, display and speakers of a radio; the ignition switch ofgas pedal of an automobile; and the card reader, keypad, display andcurrency dispenser of an automated teller machine. In one embodiment,the user interface 810 further describes access ports provided toelectronic system 800. Access ports are used to connect an electronicsystem to the more tangible user interface components previouslyexemplified. One or more of the circuit modules 600 may be a processorproviding some form of manipulation, control or direction of inputs fromor outputs to user interface 810, or of other information eitherpreprogrammed into, or otherwise provided to, electronic system 800. Aswill be apparent from the lists of examples previously given, electronicsystem 800 will often contain certain mechanical components (not shown)in addition to the circuit modules 600 and user interface 810. It willbe appreciated that the one or more circuit modules 600 in electronicsystem 800 can be replaced by a single integrated circuit. Furthermore,electronic system 800 may be a sub-component of a larger electronicsystem.

FIG. 9 shows one embodiment of an electrical device at a system level.The electronic system depicted in FIG. 9 is a memory system 900. Memorysystem 900 acts as a higher-level host that contains one or more memorymodules 700 as described above including at least one of the SSOI activeareas or the data storage device such as set forth herein in accordancewith the present invention and a memory controller 910 that may alsoinclude circuitry for the inventive partially isolated structure or thedata storage device. Memory controller 910 provides and controls abidirectional interface between memory system 900 and an external systembus 920. Memory system 900 accepts a command signal from the externalsystem bus 920 and relays it to the one or more memory modules 700 on acommand link 930. Memory system 900 provides for data input and dataoutput between the one or more memory modules 700 and external systembus 920 on data links 940.

FIG. 10 shows a further embodiment of an electronic system as a computersystem 1000. Computer system 1000 contains a processor 1010 and a memorysystem 900 housed in a computer unit 1015. Computer system 1000 is butone example of an electronic system containing another electronicsystem, i.e. memory system 900, as a sub-component. In one embodiment,the computer system 1000 contains an input/output (I/O) circuit 1020that is coupled to the processor 1010 and the memory system 900.Computer system 1000 optionally contains user interface components thatare coupled to the I/O circuit 1020. In accordance with the presentinvention a plurality partially isolated structures or data storagedevices may each be coupled to one of a plurality of I/O pads or pins1030 of the I/O circuit 1020. The I/O circuit 1020 may then be coupled amonitor 1040, a printer 1050, a bulk storage device 1060, a keyboard1070 and a pointing device 1080. It will be appreciated that othercomponents are often associated with computer system 1000 such asmodems, device driver cards, additional storage devices, etc. It willfurther be appreciated that the processor 1010, memory system 900, I/Ocircuit 1020 and partially isolated structures or data storage devicesof computer system 1000 can be incorporated on a single integratedcircuit. Such single package processing units reduce the communicationtime between the processor 1010 and the memory system 1000.

CONCLUSION

Thus has been disclosed a strained silicon-on-insulator active area thatcan be an Si/SiGe/SOI island. A process of fabricating the strainedsilicon-on-insulator active area has also been disclosed that uses anetch that forms an undercutting bubble recess. An oxidation processcompletes vertical isolation of the strained silicon-on-insulator activearea. Embodiments of the present invention relate to processes thatfacilitate the vertical isolation of the strained silicon-on-insulatoractive area and oxidation in the lateral or bubble recess.

A structure is also achieved that includes a faceted bubble recess inone embodiment. The faceted bubble recess acts to begin a verticalisolation of the strained silicon-on-insulator active area from the bulkof the substrate.

It is emphasized that the Abstract is provided to comply with 37 C.F.R.§1.72(b) requiring an Abstract that will allow the reader to quicklyascertain the nature and gist of the technical disclosure. It issubmitted with the understanding that it will not be used to interpretor limit the scope or meaning of the claims.

While the present invention has been described in connection with apreferred embodiment thereof, those of ordinary skill in the art willrecognize that many modifications and variations may be employed. Forexample, the sample dimensions and process parameters disclosed hereinmay be varied and are disclosed for the purpose of illustration and notlimitation. The foregoing disclosure and the following claims areintended to cover all such modifications and variations.

1. An article comprising: a substrate; a relaxed semiconductive siliconcompound layer disposed above and grown in direct contact with thesubstrate; a strained silicon layer disposed above and grown in directcontact with the relaxed semiconductive silicon compound layer; whereinthe strained silicon layer is laterally isolated by a shallow trenchisolation, and wherein the strained silicon layer is vertically isolatedby a thermal oxide disposed below and grown in direct contact with boththe relaxed semiconductive silicon compound layer and the substrate. 2.The article according to claim 1, wherein the relaxed semiconductivesilicon compound layer includes a SiGe compound.
 3. The articleaccording to claim 1, above the strained silicon layer, furtherincluding: a storage device.
 4. The article of claim 1, wherein thethermal oxide comprises a mini field oxide.
 5. The article of claim 1,wherein the thermal oxide comprises a high pressure oxide.
 6. Thearticle of claim 1, wherein the thermal oxide comprises a flattenedfield oxide.
 7. The article of claim 1, wherein the thermal oxidecomprises facet faces at an oxide to substrate interface.